Air compressor



J. G. SAWYER AIR COMPRESSOR Dec. 6, 1966 2 Sheets-Sheet 1 Filed Oct. 30, 1964 INV EN TOR. JamesG. Sawyer,

ATTORNEYS.

J. G. SAWYER AIR COMPRESSOR Dec. 6, 1966 2 Sheets-Sheet 2 Filed Oct. 50, 1964 INVENTOR. d/wgs G. SA YM A TTOR/VEYJ Patented Dec. 6, 1956 3,289,922 AIR COMPRESEGR James G. Sawyer, Snyder, N.Y., assignor, by mesne assignments, to Utah Construction & Mining Co., San Francisco, Calif.

Fiied Get. 30, 1954, Ser. No. 422,871 6 Claims. (Cl. 230127) This application is a continuation-in-part of my pending application Serial No. 129,476, filed August 4, 1961, now abandoned.

This invention relates generally to the compressor art, and more particularly to a new and useful centrifugal air compressor. While not limited thereto, the compressor of my invention is designed for operation under flow conditions below those at which conventional centrifugal compressors operate.

The primary object of my invention is to provide a centrifugal compressor which is simple and relatively inexpensive in construction, while being extremely durable and dependable in operation and capable of a high degree of performance for its size.

Another important object of my invention is to provide a centrifugal compressor capable of highly eflicient operation under very low flow conditions.

In one aspect thereof, a centrifugal compressor of my invention is characterized by the provision of a shaft mounted for rotation about its lengthwise axis, a rotor having a pair of plates spaced apart in the direction of the shaft axis, one of the rotor plates being connected to the shaft and mounting the rotor on the shaft for rotation therewith, the other rotor plate having a generally central air inlet opening into the rotor, the rotor having a peripheral air outlet opening between the plates, a stator encircling the rotor, the stator having an air inlet opening in radial alinement with the rotor air outlet opening, and an air outlet opening from the stator adjacent the outer periphery thereof.

In another aspect thereof, a centrifugal compressor of my invention is characterized by the provision of a rotor, and a stator mounted at the periphery of the rotor, as described above, wherein the stator comprises a pair of members spaced apart in the direction of the shaft axis and having cover portions extending radially inwardly across the rotor plates in axially spaced relation thereto, and wherein both the rotor plates, and the cover portions of the stator members, are of shallow, frustoconical form converging toward the periphery of the rotor.

The foregoing and other objects, advantages and characterizing features of a compressor of my invention will become clearly apparent from the ensuing detailed description of certain illustrative embodiments thereof, taken in conjunction with the accompanying drawings depicting the same, wherein like reference numerals denotes like parts throughout and wherein:

FIG. 1 is a somewhat schematic, longitudinal sectional view of a centrifugal air compressor constructed in accordance with my invention, taken about on line II of FIG. 2;

FIG. 2 is a transverse, half sectional view thereof, taken about on line II-1I of FIG. 1;

FIG. 3 is a fragmentary sectional view taken about on line III-III of FIG. 2;

FIG. 4 is a somewhat schematic, longitudinal quarter sectional view of another centrifugal air compressor constructed in accordance with my invention, taken about on line 44 of FIG. 6;

FIG. 5 is a view like that of FIG. 4 but showing a further modification; and

FIG. 6 is a transverse, half sectional view of the embodiment of FIG. 4, taken about on line 6-6 of FIG. 4.

Referring now in detail to the illustrative embodiment depicted in FIGS. 13 of the accompanying drawing, a compressor of my invention is provided with an enclosing shroud or housing 1 of generally cylindrical, barrel form having end members 2 and 3 which journal a shaft 4 in bearings 5 and 6, respectively. An air inlet open ing 7 is provided in end member 2, and an air outlet member 3 is provided intend member 3.

The compressor comprises a series of centrifugal rotors, generally designated 10, each having a'pair of plates '11 and 12 spaced apart in the direction of the axis of shaft 4. The front plate 11 of each rotor is provided with a central opening 13, concentric with shaft 4, and comprising an air inlet opening into the rotor between plates 11, 12. Each rear plate 12 is centrally apertured to receive shaft 4, and is connected to shaft 4 in a manner mounting the rotor 10 on the shaft for rotation therewith. This can be accomplished, for example, by the use of rotor spacers 14, and an end spacer 15, which latter bears against a shoulder 16 on the shaft. The spacers 14 extend between adjacent rotors 1i), and are held in place by a lock nut 17, whereby each rotor plate 12 is clamped to the shaft for rotation therewith, the front end spacer 14 being keyed to the shaft as indicated at 18.

The front rotor plates 11 are mounted on the associated rear rotor plates 12 by the generally radially extending rotor vanes 20, which can be provided with any desired curvature, depending upon the characteristics desired.

Thus, each rotor comprises paired plates or walls 11, 12, with the plates 12 being connected to shaft 4 and supporting each rotor thereon, and with the plates 11 held in axially spaced relation to the plates 12 by the series of vanes 20 in each rotor. The plates 11 and 12 can be joined to the directing vanes 24) by welding, or any desired means of fabrication.

An air outlet opening 21 is provided at the periphery of each rotor, between the spaced plates 11, 12. Thus, air enters each rotor through the central inlet opening 13, and is discharged peripherally through the outlet opening 21.

The stators, generally designated 22, are positioned at the periphery of the associated rotor. Each stator comprises plates or wall members 23 and 24, spaced apart in the direction of the shaft axis. The front stator member 23 extends radially outwardly to the enclosing housing 1, thereby providing the necessary barrier between successive impellers, and is positioned thereby. The rear stator member 24 terminates short of the housing, to provide an air outlet opening 25 around the outer periphery of the stator and directed rearwardly in the direction of the shaft axis.

Each stator member 23, 24 has a cover portion 26, 27, respectively, extending generally radially inwardly across the front and rear rotor plates 11, 12 respectively, to cover and enclose the same. Cover portions 26 extend radially inwardly to about the periphery of the air inlet openings 11, thereby forming a barrier to reverse air flow. The rear stator cover portions 27 extend inwardly to about the spacer members 14, 15, and also function as a barrier to reverse air flow. Thus, stator extensions 26 and 27 form an enclosing housing for the associated rotor.

Stators 22 are spaced apart by stator spacing members 28 which extend between adjacent stators, at spaced points therearound, being provided with oppositely directed, terminal flanges 29 for securing the same to the stator members. End walls 2 and 3 are removable, and. stator structures 22 and rotors 10 are removable from housing 1 through either end thereof.

As previously noted, the front stator members 23 extend outwardly to the housing 1. The rear stator members 24 are positioned axially relative to the front members by decelerating stator vanes generally designated 30, Vanes 30 preferably are paired, and fabricated from a single piece of material to provide paired vanes integral with a connecting web 31. Vanes 30 are caused to diverge outwardly, having an inlet angle matching the angle of the air as it leaves the rotor. This provides air passages of increasing cross-sectional area from the stator air inlet 32, which is positioned in radially spaced relation to the peripheral air outlet opening 21 of the associted rotor, to the stator outlet 25. As a result, the partially compressed air is decelerated sufliciently to permit loss free passage through outlet 25 to the inlet 11 of the subsequent rotor. By utilizing the entire periphery of the housing 1 for the discharge of air, there is provided a discharge passage 25 of sufiicient area to efficiently conduct the air to the next stage, all within the confines of the circular compressor housing 1. The vane webs 31 provide a convenient means of attaching the vanes to the stator members 23, as by spot welding or rivets 31.

I haveifound that, with this construction, a surprisingly efficient and powerful compressor can be provided, in a relatively small size unit capable of being fitted, for example, within the area available under the hood of a conventional truck. This particularly adapts my cornpressor for use in the arrangement disclosed in my copending application Serial No. 129,275 entitled Vehicle Mounted Air Compressor, now Patent No. 3,153,508, executed simultaneously with application Serial No. 129,476, the parent of this application, and filed on August 4, 1961. Of course, the compressor of this invention is not limited to use in such an arrangement.

For ease of fabrication and assembly, and economy in construction, I preferably form both the rotors and the stators 22 of thin sheet metal. However, the use of such thin sheet material presents a problem in strength, which is solved in the following manner.

Each rotor plate 11, 12 is constructed in a shallow, frusto-conical form, converging toward the periphery of the rotor. Similarly, each stator cover portion 26, 27 is shaped to a shallow, frusto-conical form, converging toward the rotor periphery, and joined to the working stator portions peripherally beyond the rotor by the more sharply converging connecting portions 32. This shallow, dish shaped or frusto-conical form provides the requisite structural stability, while permitting'the use of thin sheet material.

Shaft 4 is releasably held in axial position by shoulder 33 mounted between washers 34 held in housing 35, with the shaft extending therebeyond for attachment to any desired driving source.

The compressor of my invention is especially designed for operation under low flow conditions, for example in the rangeof 80-100 c.f.m. and is capable of eflicient operation at flow ranges in which conventional centrifugal compressors simply do not operate. A major factor in achieving this result is the provision of a stator having a large number of thin diffuser vanes, for example forty, located very close to the rotor tip, as shown at 30 in FIGS. 1-3 and 30' in FIGS. 4-6. Essentially only working clearance is provided between the rotor periphery and the stator inlet, the spacing therebetween being exaggerated in the drawings for greater clarity and ease of illustration.

This last factor is extremely important because the distance which the air must travel from the rotor outlet to the diffuser is critical.

When the air leaves the rotor it has a very high velocity. This velocity represents energy which must be captured by conversion to static pressure through diffusion. For efficient performance substantially all of the velocity energy of the existing air must be captured in the diffuser.

However, most of this velocity is lost in conventional low flow compressors because the diffuser vanes are spaced so far from the rotor outlet that the energy represented by l the velocity of the air leaving the rotor is dissipated before reaching the stator blades.

The distance which a stream of air can travel before its energy is dissipated is proportional to its width. In low flow compressors the rotor outlet necessarily is very narrow, with the result that air leaving the rotor is capable of traveling only a very short distance without substantial energy loss.

I avoid such energy loss by positioning the inlet ends of the diffuser vanes as close as possible to the rotor outlet. In accordance with my invention the radial clearance between the rotor outlet and the diffuser vanes is such that the air path from the rotor outlet to the inlet ends of the diffuser vanes is essentially no greater and preferably less than the distance which the air stream exiting from the rotor will travel Without substantial energy loss. To accomplish this, I provide a radial clearance which is less than 1% of the rotor diameter, for example 0.040 inch with a rotor having a diameter of 6 inches.

It is another important feature of my invention that the diffuser has a large number of closely spaced, thin blades.

Vaneless diffusers, while suitable for high flow compreasors are entirely unsuitable for a compressor operating under low flow conditions. This is because in a vaneless diffuser the air must travel its natural path wherein velocity is inversely proportional to the distance from the center of rotation. This gives good efiiciency at high flows. In a low flow compressor the width of the air stream is greatly reduced, as previously pointed out. However, the air still must travel the same distance for the same degree of diffusion. As a result, the ratio of the distance traveled to the channel width is much greater than in high flow compressors, introducing prohibitive friction losses.

Therefore, vanes are essential to a low flow diffuser. Conventional vaned diffusers have a relatively small number of relatively widely spaced blades. In a low flow diffuser the channel width is so small compared to the relatively large distance between adjacent blades that the resulting air passage is inefficient. Further the expansion angle provided by such conventional diffuser lading is such that air separation occurs under low flow conditions.

Therefore, I provide a large number of closely spaced diffuser blades, providing an eificiently proportioned passageway and an expansion angle favorable to low flow conditions. However, if too many blades are provided excessive skin friction is developed. I have determined that the optimum expansion angle is 7 to 10 degrees, requiring from 36 to 52 blades. To avoid crowding in the air passageways, I make the blades of thin sheet material. Also, the diffuser blades of my invention are essentially flat and straight, avoiding disturbances resulting from blade curvature.

While losses in the compressor are primarily those occurring within the stator, stator performance is greatly influenced by rotor design. Pressure development in the rotor is accomplished by centrifugal forces, which are not particularly disturbed by air separation or air turbulence. However, the development of pressure within the stator, representing approximately one-half the total pressure rise, is accomplished by the conversion of velocity to pressure. This is a diffusion process wherein it is difficult to maintain eflicient flow with turbulent air.

Turbulence is produced by the separation of air in the rotor. Such separation occurs at the trailing, rearward surfaces of impeller vanes 20, looking in the direction of rotor rotation. Air tends to separate and move away from the suction side of the vanes, as it moves progressively outwardly therealong. As a result, a boundary layer of relatively stagnant air tends to form along the trailing surface of impeller vanes 20. Such stagnant air produces turbulence in the air leaving the rotor.

Air separation also occurs at the inner surface of rotor plate 11. The air entering the rotor tends to separate and move away from the inner surface of rotor wall 11, resulting in an uncontrolled boundary layer of relatively stagnant air on this surface which produces additional turbulence in the air leaving the rotor.

These disturbances in the air flow from the rotor are especially detrimental on stator performance under low flow conditions, and I have found that improvement of the air flow within the rotor, While it does not particularly improve the performance of the rotor, does significantly improve the performance of the stator and results in an unexpected increase in efficiency of operation under low flow conditions.

Separation of air in the rotor and its deleterious effects on the compression effect of the stator or diffuser, are avoided in the compressor of my invention in the following mariner, reference being made to the illustrative embodiment shown in FIGS. 4, and 6. The compressor of FIGS. 46 is generally similar to that of FIGS. 1-3, comprising a series of centrifugal rotors 19' each having a pair of plates or walls 11, 12 spaced apart in the direction of the axis of shaft 4. The front wall 11 of each rotor is provided with a central air inlet opening, concentric with shaft 4 and opening into the rotor between walls 11, 12'. The front rotor walls 11' are mounted on the associated rear rotor walls 12' by generally radially extending rotor vanes which can be provided with any desired curvature, depending upon the characteristics de sired, and the rear rotor walls 12 are secured to shaft 4, as previously described.

However, whereas in the embodiment of FIGS. 1-3 the rotors have impeller vanes 29 extending generally radially from the inlet to the outlet of the rotor in a continuous and uninterrupted manner, that construction is not used in the embodiment of FIGS. 46 because of the tendency of air passing through the rotor to separate from the trailing surfaces of the rotor vanes 28. Instead, the embodiment of FIGS. 46 uses a segmented rotor vane construction, wherein each radially extending vane in fact comprises a series of vane segments 20' extending from the inlet of the rotor to the outlet in radially stepped, overlapping, circumferentially spaced relation as clearly illustrated in FIGS. 4 and 6. The inner ends of the outer segments overlap the outer ends of the inner segments, on the leading faces thereof, at locations therealong where separation of air normally would start to occur.

As a result of this segmented impeller vane construction air passing through the rotor along the leading faces of the vane segments exists between adjacent segments onto the trailing surfaces thereof. Such exiting air thereby passes from the space between one pair of segmented vanes into the space between the succeeding pair thereof. In doing this it is directed across the trailing surfaces of the outer segments in a manner avoiding the stagnant boundary layer of air which tends to form thereon. This provides a boundary layer control over the impeller vanes.

However, the problem of air separation from the front rotor walls 11 remains, and is perhaps even more severe. This problem is avoided, in the embodiment of FIGS. 46, by the provision of annular air deflectors 36 and 37 in the rotor air inlet opening. Deflectors 36, 37 are concentric with each other and with shaft 4. Also, they are of semi-circular, transverse sectional form, being curved about their annular axes, as clearly illustrated in FIGS. 4 and 5. Deflector rings 36 are mounted along their outer, upper sides on the lower end of front stator skirts 26', and curve downwardly, inwardly and then upwardly, terminating in closely spaced relation to the lower edge of the front rotor wall 11', leaving only working clearance therebetween.

Deflector rings 37 are positioned, in the illustrated embodiment, approximately midway between deflectors 36 and spacing collars 14, having upwardly curving ends positioned one adjacent the bottom edge of the inner vane segments 29', in closely spaced relation thereto with substantially only working clearance therebetween, and the other between adjacent pairs of stators 22', as shown in FIG. 4. Deflectors 37 are carried by deflectors 36, being mounted thereon by connecting web plates 38 spaced around shaft 4, being for example four in number and extending axially of shaft 4 for minimum interference with air flow through the rotor inlet.

Thus, deflectors 36, 37 provide rotor inlet passages having radially directed inlets receiving air passage between adjacent rotor-stator assemblies, and radially directed outlets into the rotors. As a result of thus deflecting and directing the inlet air to rotors 10', the inlet air is controlled and there is provided a stream of air directed along the inner face of rotor walls 11'. This provides a boundary layer control avoiding the layer of stagnant air which otherwise tends to form on that surface.

While separation of air along the impeller vanes and separation of air along the rotor wall have been dealt with individually, they are not separate and distinct but are inter-related. The segmented impeller construction and rotor inlet deflector arrangement, and particularly 7 the latter, in combination with the stator of my invention provides for a high efficiency of operation even under low flow conditions where conventional centrifugal compressors do not operate well, if at all. The control of air entering the rotor, when combined with a stator of my invention, produces an unexpectedly high increase in efficiency, on the order of 10%, to provide a centrifugal compressor operable at 80400 c.f.n1. with an efiiciency on the order of 70%.

As in the embodiment of FIGS. 1-3, that of FIGS. 46 can be a sheet metal fabrication. The converging rotor walls provide a substantially constant air passage area, for substantially constant velocity in the rotor. Diffusion therefore is substantially confined to the stator, which is designed to produce compression rise through diffusion where as the rotor is not.

Where input power and barrel diameter are not limiting factors more efficient flow and greater pressure rise can be achieved by extending the rotor Walls beyond the impeller blades, as shown at 39 in FIG. 5. This provides a partial diffusion under conditions of substantially no relative velocity. The distance traveled by the air in relation to its surrounding walls 39 is relatively short. Therefore, the difiusion efficiency is very high.

Accordingly, it is seen that my invention fully accomplishes its intended objects. Centrifugal compressors intended for low flow operation present problems very different from those found in high flow compressors and require different solutions. My invention solves these problems, and provides a centrifugal compressor capable of extremely high performance, producing for example 100 psi. at -100 c.f.m. using rotors only 6" in diameter and of inexpensive sheet metal construction. While I have disclosed and described in detail only certain selected embodiments, that has been done by way of illustration without thought of limitation. I am aware that modifications and variations will occur to those skilled in the art, and intend to include the same Within the scope of the appended claims.

Having fully disclosed and completely described my invention, and its mode of operation, what I claim as new 1. A centrifugal compressor comprising a shaft mounted for rotation about its lengthwise axis, a rotor having a pair of sheet metal plates spaced apart in the direction of said axis, one of said plates being connected to said shaft and mounting said rotor on said shaft for rotation therewith, the other of said plates having a generally central air inlet opening therethrough into said rotor, said rotor having a peripheral air outlet opening between said plates, a stator encircling said rotor, said stator having a pair of substantially parallel sheet metal members spaced apart in the direction of said axis, an air inlet opening between. said members in radial alinement with said rotor air outlet opening, an air outlet opening from said stator adjacent the outer periphery thereof, and a series of rectilinear decelerating vanes between said members in spaced apart relation around said axis, said vanes defining air passages therebetween of continuously increasing cross-sectional area from said stator air inlet opening to said stator outlet opening, wherein said stator members extend radially inwardly across said rotor plates in axially spaced relation thereto, and wherein both said rotor plates and the portions of said stator members extending across said rotor plates are of shallow, frustoconical form converging toward the periphery of said rotor.

2. A centrifugal compressor comprising a rotor mounted for rotation about an axis and having a pair of sheet material plates spaced apart in the direction of said axis, said rotor having a generally central air inlet opening and a peripheral air outlet opening, and a stator encircling said rotor, said stator having a pair of substantially parallel sheet material members spaced apart in the direction of said axis by rectilinear decelerating vanes, an air inlet opening between said members in radial alinement with said rotor air outlet opening, and an axially directed air outlet opening from said stator adjacent the outer periphery thereof, wherein said rotor plates are spaced apart by air directing vanes therebetween, and are of shallow, generally conical form converging toward the periphery of said rotor, and wherein said stator members have cover portions extending radially inwardly across said rotor plates in axially spaced relation thereto, said stator member cover portions being of shallow, generally conical form converging toward the periphery of said rotor.

3. A centrifugal compressor comprising a shaft mounted for rotation about its lengthwise axis, a rotor having a pair of sheet metal plates spaced apart in the direction of said axis, one of said plates being connected to said shaft and mounting said rotor on said shaft for rotation therewith, the other of said plates having a generally central air inlet opening therethrough into said rotor, said rotor having a peripheral air outlet opening between said plates, a stator encircling said rotor, said stator having a pair of substantially parallel sheet metal members spaced apart in the direction of said axis, an air inlet opening between said members in radial alinement with said rotor air outlet opening, an air outlet opening from said stator adjacent the outer periphery thereof, and a series of rectilinear decelerating vanes between said members in spaced apart relation around said axis, said vanes defining air passages therebetween of continuously increasing crosssectional area from said stator air inlet opening to said stator outlet opening, wherein said stator members extend radially inwardly across said rotor plates in axially spaced relation thereto, and wherein at least one of said rotor plates and the portion of the stator member extending thereacross are of shallow, frusto-conical form, said rotor plates and the portions of said stator members extending thereacross converging toward the periphery of said rotor.

4. A centrifugal compressor comprising a shaft mounted for rotation about its lengthwise axis, a sheet metal rotor mounted upon said shaft for rotation therewith and having a pair of walls spaced apart in the direction of said axis, one of said walls having a generally central air inlet opening therethrough into said rotor, said rotor having a peripheral air outlet opening between said walls, air directing vanes between said rotor walls extending substantially from said rotor inlet opening to said rotor outlet opening in spaced apart relation around said axis, a sheet metal stator encircling said rotor and having a pair of wall members spaced apart in the direction of said axis, an air inlet opening between said stator wall members in closely spaced radial alinement with said rotor outlet opening, an air outlet opening from said stator adjacent the periphery thereof, substantially flat plate decelerating vanes in fixed position between said stator walls extending substantially rectilinearly from said stator inlet opening at the periphery of said rotor to said stator outlet opening in outwardly divergent closely spaced relation around said axis and at an angle of about 10 to the periphery of said rotor, and concentric annular deflecting vanes positioned in spaced apart relation across said rotor air inlet opening, providing multiple annular inlet passages, said deflector vanes being curved for directing entering air radially into said rotor.

5. A compressor as defined in claim 3 wherein said decelerating vanes extend in a generally tangential fixed direction outwardly from substantially the periphery of said rotor; and annular deflecting vanes in said inlet opening and arranged to direct incoming air radially into said rotor.

6. A compressor as defined in claim 3 including impeller vanes extending between said rotor plates, each impeller vane comprising radially spaced segments arranged with their ends in overlapping and circumferentially spaced relation to the ends of adjacent segments.

References Cited by the Examiner UNITED STATES PATENTS 835,570 11/1906 Spencer 230-130 1,075,300 10/1913 Moss 103-111 1,158,738 11/1915 Spencer 230-130 1,263,056 4/1918 Graemiger 230- 1,288,728 12/1918 Spencer 230- 1,633,609 6/1927 Schmidt 230-134 1,745,854 2/1930 Lawaczeck 103-108 2,139,112 12/1938 Catranis 230-130 2,366,964 1/ 1945 Howard 103-108 2,641,191 6/1953 Buchi 103-111 2,671,604 3/1954 Hagen 230-130 2,899,129 8/1959 Schwaiger 230-134.45 2,932,444 4/ 1960 Walker 230-117 FOREIGN PATENTS 43 5,755 3/ 1912 France.

889,341 9/ 1943 France.

971,515 7/ 1950 France. 1,113,658 12/1955 France. 1,227,952 3/ 1960 France.

581,164 3/1931 Germany.

419,544 11/ 1934 Great Britain.

604,744 5/1960 Italy.

MARK NEWMAN, Primary Examiner.

HENRY F. RADUAZO, SAMUEL LEVINE, Examiners. 

1. A CENTRIFUGAL COMPRESSOR COMPRISING A SHAFT MOUNTED FOR ROTATION ABOUT ITS LENGTHWISE AXIS, A ROTOR HAVING A PAIR OF SHEET METAL PLATES SPACED APART IN THE DIRECTION OF SAID AXIS, ONE OF SAID PLATES BEING CONNECTED TO SAID SHAFT AND MOUNTING SAID ROTOR ON SAID SHAFT FOR ROTATION THEREWITH, THE OTHER OF SAID PLATES HAVING A GENERALLY CENTRAL AIR INLET OPENING THERETHROUGH INTO SAID ROTOR, SAID ROTOR HAVING A PERIPHERAL AIR OUTLET OPENING BETWEEN SAID PLATES, A STATOR ENCIRCLING SAID ROTOR, SAID STATOR HAVING A PAIR OF SUBSTANTIALLY PARALLEL SHEET METAL MEMBERS SPACED APART IN THE DIRECTION OF SAID AXIS, AN AIR INLET OPENING BETWEEN SAID MEMBERS IN RADIAL ALINEMENT WITH SAID ROTOR AIR OUTLET OPENING, AN AIR OUTLET OPENING FROM SAID STATOR ADJACENT THE OUTER PERIPHERY THEREOF, AND A SERIES OF RECTILINEAR DECELERATING VANES BETWEEN SAID MEMBERS IN SPACED APART RELATION AROUND SAID AXIS, SAID VANES DEFINING AIR PASSAGES THEREBETWEEN OF CONTINUOUSLY INCREASING CROSS-SECTIONAL AREA FROM SAID STATOR AIR INLET OPENING TO SAID STATOR OUTLET OPENING, WHEREIN SAID STATOR MEMBERS EXTEND RADIALLY INWARDLY ACROSS SAID ROTOR PLATES IN AXIALLY SPACED RELATION THERETO, AND WHEREIN BOTH SAID ROTOR PLATES AND THE PORTIONS OF SAID STATOR MEMBERS EXTENDING ACROSS SAID ROTOR PLATES ARE OF SHALLOW, FRUSTOCONICAL FORM CONVERGING TOWARD THE PERIPHERY OF SAID ROTOR. 